/*
 *  linux/init/main.c
 *
 *  (C) 1991  Linus Torvalds
 */

#define __LIBRARY__
#include <unistd.h>
#include <time.h>

/*
 * we need this inline - forking from kernel space will result
 * in NO COPY ON WRITE (!!!), until an execve is executed. This
 * is no problem, but for the stack. This is handled by not letting
 * main() use the stack at all after fork(). Thus, no function
 * calls - which means inline code for fork too, as otherwise we
 * would use the stack upon exit from 'fork()'.
 *
 * Actually only pause and fork are needed inline, so that there
 * won't be any messing with the stack from main(), but we define
 * some others too.
 */
static inline fork(void) __attribute__((always_inline));
static inline pause(void) __attribute__((always_inline));
static inline _syscall0(int,fork) // corresponding to fork()
static inline _syscall0(int,pause)
static inline _syscall1(int,setup,void *,BIOS)
static inline _syscall0(int,sync)

#include <linux/tty.h>
#include <linux/sched.h>
#include <linux/head.h>
#include <asm/system.h>
#include <asm/io.h>

#include <stddef.h>
#include <stdarg.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>

#include <linux/fs.h>

static char printbuf[1024];

extern int vsprintf();
extern void init(void);
extern void blk_dev_init(void);
extern void chr_dev_init(void);
extern void hd_init(void);
extern void floppy_init(void);
extern void mem_init(long start, long end);
// ram disk initialization
extern long rd_init(long mem_start, int length); //dir: kernel/ramdisk.c, rd_init = ramdisk init
extern long kernel_mktime(struct tm * tm);
extern long startup_time;

/*
 * This is set up by the setup-routine at boot-time
 */

//extended memory size at mem address 0x90002
#define EXT_MEM_K (*(unsigned short *)0x90002)
// drive information struct
#define DRIVE_INFO (*(struct drive_info *)0x90080)
#define ORIG_ROOT_DEV (*(unsigned short *)0x901FC)

/*
 * Yeah, yeah, it's ugly, but I cannot find how to do this correctly
 * and this seems to work. If anybody has more info on the real-time
 * clock I'd be interested. Most of this was trial and error, and some
 * bios-listing reading. Urghh.
 */

// read CMOS time
#define CMOS_READ(addr) ({ \
outb_p(0x80|addr,0x70); \
inb_p(0x71); \
})

#define BCD_TO_BIN(val) ((val)=((val)&15) + ((val)>>4)*10)

static void time_init(void) {
    struct tm time;

    do {
        time.tm_sec = CMOS_READ(0);
        time.tm_min = CMOS_READ(2);
        time.tm_hour = CMOS_READ(4);
        time.tm_mday = CMOS_READ(7);
        time.tm_mon = CMOS_READ(8);
        time.tm_year = CMOS_READ(9);
    } while (time.tm_sec != CMOS_READ(0));
    BCD_TO_BIN(time.tm_sec);
    BCD_TO_BIN(time.tm_min);
    BCD_TO_BIN(time.tm_hour);
    BCD_TO_BIN(time.tm_mday);
    BCD_TO_BIN(time.tm_mon);
    BCD_TO_BIN(time.tm_year);
    time.tm_mon--;
    startup_time = kernel_mktime(&time); //from 1970/1/1
}

static long memory_end = 0;
static long buffer_memory_end = 0;
static long main_memory_start = 0;

struct drive_info { char dummy[32]; } drive_info;
//This is really void
void main(void){
/* The startup routine assumes (well, ...) this */
/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */

    //Set up root device and hard disk
     ROOT_DEV = ORIG_ROOT_DEV;
     drive_info = DRIVE_INFO;

    //Setup the position and size of main memory and buffer.according to
    //memory size
    memory_end = (1<<20) + (EXT_MEM_K<<10); //1MB + extended memory is the total memory size
    memory_end &= 0xfffff000; //Integral pages, ignore the remaining part that is less than a page
    if (memory_end > 16*1024*1024)
        memory_end = 16*1024*1024;
    if (memory_end > 12*1024*1024)
        buffer_memory_end = 4*1024*1024;
    else if (memory_end > 6*1024*1024)
        buffer_memory_end = 2*1024*1024;
    else
        buffer_memory_end = 1*1024*1024;
    //Main memory comes after buffer memory
    main_memory_start = buffer_memory_end;

    //check the RAMDISK flag in makefile, set ram disk if exist
#ifdef RAMDISK
    main_memory_start += rd_init(main_memory_start, RAMDISK*1024);
#endif
    // initialize memory management structure
    mem_init(main_memory_start,memory_end);

    trap_init();                     // interruption initialization
    blk_dev_init();                  // block devices initialization.
    chr_dev_init();                  // character devices initialization, display and keyboard
    tty_init();                      // serial ports initialization (rs232 protocol)
    time_init();                     // read CMOS time and initialize startup time
    sched_init();                    // Schedule initialization
    buffer_init(buffer_memory_end);  // initialize the buffer
    hd_init();                       // initialize hard disk
    floppy_init();                   // initialize floppy disk.
    sti();                           // setup interruption  (re-enable)
    move_to_user_mode();             // from privilege level 0 to 3
    if (!fork()) {        /* we count on this going ok */
        init();
    }
/*
 *   NOTE!!   For any other task 'pause()' would mean we have to get a
 * signal to awaken, but task0 is the sole exception (see 'schedule()')
 * as task 0 gets activated at every idle moment (when no other tasks
 * can run). For task0 'pause()' just means we go check if some other
 * task can run, and if not we return here.
 */
    for(;;) pause();
}

static int printf(const char *fmt, ...)
{
    va_list args;
    int i;

    va_start(args, fmt);
    write(1,printbuf,i=vsprintf(printbuf, fmt, args));
    va_end(args);
    return i;
}

static char * argv_rc[] = { "/bin/sh", NULL };
static char * envp_rc[] = { "HOME=/", NULL };

static char * argv[] = { "-/bin/sh",NULL };
static char * envp[] = { "HOME=/usr/root", NULL };

void init(void)
{
    int pid,i;

    setup((void *) &drive_info);
    (void) open("/dev/tty0",O_RDWR,0);
    (void) dup(0);
    (void) dup(0);
    printf("%d buffers = %d bytes buffer space\n\r",NR_BUFFERS,
        NR_BUFFERS*BLOCK_SIZE);
    printf("Free mem: %d bytes\n\r",memory_end-main_memory_start);
    if (!(pid=fork())) {
        close(0);
        if (open("/etc/rc",O_RDONLY,0))
            _exit(1);
        execve("/bin/sh",argv_rc,envp_rc);
        _exit(2);
    }
    if (pid>0)
        while (pid != wait(&i))
            /* nothing */;
    while (1) {
        if ((pid=fork())<0) {
            printf("Fork failed in init\r\n");
            continue;
        }
        if (!pid) {
            close(0);close(1);close(2);
            setsid();
            (void) open("/dev/tty0",O_RDWR,0);
            (void) dup(0);
            (void) dup(0);
            _exit(execve("/bin/sh",argv,envp));
        }
        while (1)
            if (pid == wait(&i))
                break;
        printf("\n\rchild %d died with code %04x\n\r",pid,i);
        sync();
    }
    _exit(0);    /* NOTE! _exit, not exit() */
}
